1. Field of the Invention
The present invention relates to an exposure apparatus and an exposure method, and in particular relates to an exposure apparatus, an exposure method and a method for manufacturing devices, which are used at the time of manufacturing circuit devices for semiconductor elements or liquid crystal display elements and the like using a lithography process.
2. Description of the Related Art
At present, in manufacturing factory for semiconductor devices, circuit devices (64 megabit D-RAM and the like) with a minimum line width of around 0.3 to 0.35 xcexcm are being mass produced using a reducing projection exposure apparatus, namely a so called stepper, with i-line of a mercury vapor lamp of 365 nm wavelength as the illumination light. At the same time, the introduction of exposure apparatus for mass production manufacture of next generation circuit devices with minimum line widths of less than 0.25 xcexcm, having integration of the 256 megabit or 1 gigabit bit D-RAM class, has commenced.
As the exposure apparatus used in next generation circuit device manufacture, development is being carried out of a step-and-scan type scanning exposure apparatus, with ultraviolet pulse laser radiation of 248 nm wavelengths from a KrF excimer laser light source, or ultraviolet pulse laser radiation of 193 nm wavelengths from an ArF excimer laser light source as the illumination light. In the step-and-scan type scanning exposure apparatus, a scanning exposure operation and an inter-shot stepping operation are repeated, and at the time of scanning, a mask or reticle (hereunder referred to as xe2x80x9creticlexe2x80x9d) on which a circuit pattern is drawn, and a wafer serving as a photosensitive substrate are one dimensionally scanned relatively with respect to a projection field of a reducing projection optical system. As a result, the whole of the circuit pattern of the reticle is transferred to inside one shot region on the wafer.
However, the integration of semiconductor devices is moving prospectively to even higher integration of from 1 gigabit to 4 gigabits. The device rule in this case become 0.1 xcexcm, that is around 100 nmL/S, and to correspond to this with an exposure apparatus using ultraviolet pulse laser radiation of the aforementioned 193 nm wavelength as the exposure light, there are numerous technical problems.
Recently, the development of an EUV exposure apparatus which uses radiation of the soft X-ray region of 5 to 15 nm wavelength (referred to in the specification of this invention as xe2x80x9cEUV (Extreme Ultra Violet) radiationxe2x80x9d) is starting to be reached. This EUV exposure apparatus is gaining attention as an effective candidate for next generation exposure apparatus for minimum line widths, where for example with a line-and-space-pattern the pitch thereof is from 100 nm to 70 nm.
However, in such an EUV exposure apparatus, the projection optical system thereof comprises only reflecting type optical elements (mirrors). With such optical elements, the reflectivity is around 60 to 70%. Consequently, the optical elements are heated by the remaining 30 to 40% of energy. If the optical elements are heated, then deformation such as positional displacement and curvature change occur in the reflecting surface due to this, so that the projection optical system changes, resulting in the problem that an adverse effect is exerted on the exposure characteristics.
To address such a problem, cooling by convection of air cannot be hoped for since the projection optical system is in a vacuum. Consequently, conventionally a cooling mechanism is arranged on the attachment part or the rear side or the like of the optical elements, to cool the optical elements and thus suppress changes in the projection optical system.
However, this countermeasure is only for suppressing changes in the respective optical elements constituting the projection optical system, and it is not addressed to correction should a change once occur.
Moreover, in the EUV exposure apparatus, because the illumination optical system is constructed only from a plurality of reflecting type optical elements, there is the risk that a drop in optical characteristics of the illumination optical system may occur due to a change in the reflection surface of the optical elements.
It is an object of the present invention to provide an exposure apparatus and exposure method which, even if a change occur in a projection optical system and/or an illumination optical system, can correct the change in order to maintain superior exposure characteristics. It is also an object of the present invention to provide a device manufacturing method which can manufacture stabilized high quality devices using the above exposure apparatus and exposure method.
In order to achieve the abovementioned objects, the exposure apparatus of the present invention is an exposure apparatus which illuminates a pattern formed on a mask with exposure light to transfer the pattern onto a substrate by way of a projection optical system. The projection optical system has at least one reflection type optical element, and is provided with a detection device that detects position information at an irradiation position of the exposure light on the reflection type optical element, and a correction device that corrects the optical element based on the position information.
In the exposure apparatus of the present invention, by detecting with the detection device the irradiation position of the exposure light on the reflection type optical element which constitutes the projection optical system, then position information such as the position, inclination, and deformation of the reflection type optical element can be obtained. Then based on this position information, the position, inclination, deformation and the like of the optical element is corrected with the correction device, thereby enabling the optical element to be corrected to a correct condition. Consequently, even in the case where for example due to heat or the like, the respective optical elements constituting the projection optical system change, these can be corrected. Hence the inherent exposure characteristics can be maintained enabling stabilized exposure to be performed.
In another aspect of the present invention, the detection device detects position information at a plurality of positions with respect to a single reflection type optical element. Therefore, position information for the inclination, deformation or the like of the optical element can also be obtained, and higher accuracy correction is possible.
In another aspect of the present invention, the mask is a reflecting type. Furthermore, in another aspect of the present invention, the exposure light is extreme ultraviolet (EUV) light, and the optical elements which constitute the projection optical system are all reflection type optical elements. As a result, EUV radiation can be used as the exposure light, and high accuracy transfer of extremely fine patterns, for example of fine L/S patterns of from 100 nm to below this, or isolated patterns of 70 nm or below this, are possible. By providing the change correction function of the projection optical system in this exposure apparatus, performance maintenance thereof can be easily affected.
In another aspect of the present invention, an interferometer is provided as the detection device. Hence the position change of the optical element can be measured without requiring contact.
Furthermore, in another aspect of the present invention, the measuring beam of the interferometer is irradiated orthogonal to a reflection surface of the optical element. As a result, position information for the same place as the irradiated position of the illumination light on the optical element can be measured with the interferometer. Hence high accuracy measurement can be performed. Moreover, by irradiating the measuring beam orthogonal to the reflection face of the optical element, the number of turn up mirrors or the like positioned on the optical path of the measuring beam can be kept to a minimum. Furthermore, if turn up mirrors are provided on a single base member together with reference mirrors for a reference beam, then measurement of changes in the relation of the relative positions of the plurality of reflection type optical elements constituting the projection optical system can be assured.
Another aspect of the present invention comprises, as the correction device, an actuator that corrects a position or shape or the like of the optical element. In this way, by driving an actuator such as a piezo element or the like to apply a required stress to the optical element, the movement, attitude, shape or the like of the optical element can be corrected by a required dimension.
Another aspect of the present invention further comprises a movable body arranged on an image surface side of the projection optical system, and a measuring device that measures the optical characteristics of the projection optical system, and the measuring device comprises a light receiving face which detects the exposure light and arranged on the movable body. Furthermore, the movable body may be a substrate stage. The measuring device may be a device for measuring at least the wave front aberration of the optical characteristics of the projection optical system. Moreover, the measuring device may have a point-diffraction interferometer.
If the optical characteristics of the projection optical system are measured periodically with the measuring device, then the residual error of the optical characteristics which cannot be corrected by the adjustment of the optical elements by means of the correction device only, can be detected. Then based on the detection result, the optical elements can be adjusted by the correction device and the residual error can be corrected.
Another aspect of the present invention further comprises a stage system which relatively moves the substrate with respect to the irradiating exposure light while relatively moving the mask with respect to the exposure light in a synchronous manner, to thereby scan expose the substrate with the exposure light. In this case, in the step-and-scan type exposure apparatus, the aforementioned affect can be obtained.
Another aspect of the present invention is an exposure method where a pattern formed on a mask is illuminated with exposure light and transferred onto a substrate by way of a projection optical system incorporating at least one reflection type optical element. The position information regarding an irradiation position of the exposure light on the reflection type optical element is detected by a detection device, and the optical element is corrected by a correction device based on the position information.
According to such an exposure apparatus and exposure method, by detecting with the detection device the irradiation position of the exposure light on the reflection type optical element which constitutes the projection optical system, then position information such as the position, inclination, and deformation of the reflection type optical element can be obtained. Then based on this position information, the position, inclination, deformation and the like of the optical element is corrected with the correction device, thereby enabling the optical element to be corrected to a correct condition.
Another aspect of the present invention detects the irradiation position of the exposure light on the reflection type optical element constituting the projection optical system by the detection device. As a result, the position information such as the position, inclination, and deformation of the reflection type optical element can be obtained. Then based on this position information, the position, inclination, deformation and the like of the optical element can be corrected with the correction device. Hence the optical element can be corrected to a correct condition. Consequently, even in the case where for example due to heat or the like, the respective optical elements constituting the projection optical system change, these can be corrected. Hence the inherent exposure characteristics can be maintained enabling stabilized exposure to be performed.
In another aspect of the present invention, wave front aberration of the transmission light of the projection optical system is detected by an aberration detection device, and the optical element corrected based on the detection result. If this correction of the transmission light by wave front aberration detection is carried out for example at the time of installing the exposure apparatus, then assurance of the exposure performance at the initial state can be obtained. In addition, by performing at appropriate intervals the correction of the reflection type optical element using the position information, maintenance of the exposure performance is facilitated.
A device manufacturing method of another aspect of the present invention includes a step for transferring a device pattern onto a photosensitive substrate using the aforementioned exposure apparatus. By manufacturing a device with such an exposure apparatus, the device pattern is transferred onto the photosensitive substrate in a condition with the intrinsic exposure performance of the projection optical system maintained. Consequently, devices of a predetermined quality can be stably manufactured.